For example, in a process of manufacturing a semiconductor device, a liquid crystal display or the like, various processes such as film formation, etching, oxidation and the like are performed on a semiconductor substrate or a substrate for use in liquid crystal display (hereinafter, simply referred to as “wafer”) in separate processing apparatuses. When a wafer is loaded into and unloaded from a processing apparatus, a transfer unit having a transfer arm for holding the wafer is generally used.
The transfer unit is provided in, e.g., the processing apparatus. The transfer unit needs to accurately transfer the wafer to a wafer delivery unit including a plurality of support pins. Especially, a wafer transfer position of the transfer arm needs to be accurately aligned with a height position of leading ends of the support pins at the time of contact with the wafer on the transfer arm, i.e., a support position of the support pins. When the transfer position of the transfer arm is not accurately aligned with the support position of the support pins, the wafer may interfere with the transfer arm or the support pins, or the wafer may not be delivered to the transfer arm or the support pins.
However, during the operation of the transfer unit, the transfer arm does not access the accurate transfer position due to various errors such as manufacturing errors of components of the transfer arm, installation errors of the respective components, assembly errors of the transfer unit, and the like, which results in deviation from the accurate transfer position. Also, the support pins may be deviated from the accurate support position for the same reason.
Therefore, in a conventional case, a teaching (transfer teaching) operation for a delivery position of a wafer in a vertical direction is performed before the actual transfer of the wafer. The teaching operation may employ various methods.
For example, Japanese Patent Application Publication No. 2003-218186 suggests a technique for teaching a delivery position of a wafer to a transfer arm by using a teaching jig. The jig is a circular plate having substantially the same size as that of the wafer. A camera and an optical sensor are provided at the circular plate. In that case, the circular plate that is the jig is transferred to a position above a mounting table in a state where a peripheral portion of the circular plate is held by the transfer arm. Then, the circular plate is relatively moved within a horizontal plane, and the camera monitors the relative movement. The center of the circular plate is made to coincide with a known central target. Then, the circular plate is relatively moved in a vertical direction, and leading ends of support pins are detected by the optical sensor. A position obtained by relatively moving the transfer arm with respect to the circular plate by a distance exceeding at least a thickness of the transfer arm from the detected positions of the leading ends of the support pins is calculated by operation. The position thus obtained is taught as a wafer delivery position to the transfer arm.
In addition, for example, Japanese Patent Application Publication No. H11-163086 suggests a teaching jig having two optical sensors. In that case, the jig is set at an arm and the arm is made to access wafer delivery parts (support pins). As a consequence, the support pins and the jig are in a close state. At this time, the optical sensors sense the support pins. The arm is moved in ±θ, ±X and +Z directions, and positions at which the respective optical sensors become ON⋅OFF are stored as positional information. An accurate transfer position to be accessed by the arm is set based on the positional information on the θ-axis, X-axis and Z-axis.
Although a general apparatus has a sensor for sensing a horizontal position of a wafer, it is difficult to perform teaching of a delivery position of the wafer in a vertical direction by the sensor. Therefore, the teaching jig is required in a conventional case as described in Japanese Patent Application Publication Nos. 2003-218186 and H11-163086. However, in the case of using the teaching jig, a teaching becomes complicated and a cost is increased. Therefore, the teaching of the wafer delivery position needs to be improved.